Many laboratory procedures require that a sterile fluid be filtered and stored within a bottle. It has been found to be advantageous to employ a sterile disposable vacuum assisted filter funnel for such procedures. Typically, the filter funnel attaches to the opening of the bottle and air is withdrawn from the bottle so as to increase the rate of filtration by increasing the pressure drop across the filter. The bottle top filter is one type of vacuum assisted filter funnel.
A prior art filter funnel having shared features with the present invention is described in U.S. Pat. No. 4,301,010 (Eddleman et al.). Eddleman describes a vacuum assisted filter funnel for drawing filtrate into a bottle. The Eddleman device includes a vacuum plenum (vacuum intake member) connectable to a vacuum source. During a filtration procedure, the Eddleman device is first sealed to the mouth of a bottle. The vacuum source is then engaged and fluid is introduced into the funnel. The bottle will be partially evacuated as air is drawn from the bottle into the vacuum plenum. This partial vacuum will tend to draw filtrate from the filter funnel into the bottle, thereby increasing the filtration flow rate. The vacuum plenum of the Eddleman device acts as a buffer against rapid pressure changes between the bottle and the vacuum source. If air is suddenly introduced into an evacuated bottle, a relatively large transient of air flow may be drawn into the vacuum plenum.
Another prior art filter funnel having shared similarity with both the present invention and the above Eddleman device is marketed by Becton Dickinson Inc., N.J., viz. the `Bottle Top Filter,` Cat. No. 7104-Falcon (.TM.). Like the Eddleman device, but unlike the present invention, the Becton Dickinson device includes a vacuum plenum. However, like the present invention, the Becton Dickinson device employs a planar horizontal gasket which seals the device onto the lip of a bottle. This planar horizontal gasket attaches to the bottom of the vacuum plenum and encircles both a funnel tube and an ingress port. The ingress port faces the interior of the bottle for drawing air from the bottle into the vacuum plenum. Also like the present invention, the Becton Dickinson device includes an outer skirt which encircles the outer perimeter of the above gasket. This outer skirt serves as a guide for centering the engagement of wide necked bottles with the gasket. Without the outer skirt, the device could be placed off center onto a wide mouth bottle so as to fail to fully engage the gasket. The outer skirt of the Becton Dickinson device serves to prevent such off centered placement. Unlike the present invention, the Becton Dickinson device lacks an inner skirt for centering the placement of the device onto small mouthed bottles.
Another prior art filter funnel having shared features with the present invention is described in U.S. Pat. No. 4,251,366 (Simon et al.). The Simon device is distinguished from the present invention because the Simon device includes an adapter to seal and to mechanically retain the device onto the top of a bottle. This adapter is engaged to the bottle by means of screw threads; in turn, the filter funnel of the Simon device is then engaged onto this adapter by means of a gasket. The Simon device is further distinguished from the present invention because its funnel tube terminates within a vacuum plenum and discharges the filtrate therein. In contrast, the tube of the funnel of the present invention passes directly into a bottle. Also, the device of the present invention lacks a vacuum plenum.
The present invention teaches that it is sometimes undesirable to buffer against sudden pressure changes between the bottle and the vacuum source. The present invention teaches that the presence of a vacuum plenum between the vacuum source and the bottle may be unnecessary and undesirable. The present invention is structurally and functionally distinguished from the prior art by the absence of the vacuum plenum.